1. Field of the Invention
Injection systems that are connected to a high-pressure accumulation chamber use pressure-controlled injectors whose control elements can be actuated electromagnetically. In such injection systems for fuel under extremely high pressure, if an overlap occurs between the open high-pressure region and the outlet-side leakage oil bore, this results in a considerable decrease in efficiency of injection systems embodied in this manner. Therefore, short circuits between the open high-pressure side inlet from the high-pressure accumulation chamber and outlet-side leakage oil bores should absolutely be prevented.
2. Description of the Prior Art
DE 198 35 494 A1 relates to a unit injector system which serves to supply fuel to the combustion chamber of directly injected internal combustion engines having a pump unit for building up an injection pressure and for injecting the fuel into the combustion chamber by way of an injection nozzle. The control unit contains a control part that is embodied as a valve that opens outward. Furthermore, a valve actuation device is provided for regulating the pressure build-up in the pump unit.
In order to create a unit injector system that is embodied in a simple design and has smaller outer dimensions, the valve actuation device is embodied as a piezoelectric actuator. In particular, this measure allows for extremely short response times.
Leakage losses that occur in injection systems significantly reduce the injection pressures that can be achieved and thus considerably reduce the efficiency of such systems.
The advantages that can be achieved with the embodiment according to the invention has the chief advantage over the prior art that a leakage of highly-pressurized fuel can now be effectively prevented through discharging it into outlet-side discharge bores in the injector body during the opening phase of the seat valve. The efficiency of an injection system that is provided with the injector embodied according to the invention can thus be significantly increased. In the embodiment proposed according to the invention, an overlap phase between the open inlet line from the high-pressure accumulation chamber (common rail) and the open leakage oil outlet does in fact occur, but the highly pressurized fuel coming into the valve control chamber is prevented from being discharged directly into the outlet-side discharge bores by virtue of the fact that suitable sealing surfaces are provided.
According to one embodiment of the concept underlying the invention, the total lift path of the control part can be extended and a slide valve with a short lift length can be disposed preceding the seat valve on the high-pressure side. The total lift of the control part is extended by this short lift length. When the seat valve is closed, a longer lift length assures that an overlap will occur on the seat face of the valve. The above-mentioned short lift length increases the lift length of the seat valve htot so that, when it is opened, no bypass occurs from the high-pressure inlet to the outlet-side leakage oil bores. The control edges on the sealing surface and the valve housing assure that the outlet-side leakage oil bores are always sealed as soon as the inlet opens the inlet lines from the high-pressure accumulation chamber.
In an alternative embodiment of the concept underlying the invention, a supplementary piston can be movably disposed on the control part. When the control part is actuated, the supplementary piston executes a movement oriented counter to its actuation direction which, by means of the fuel coming into the valve chamber under extremely high pressure, is effected so that a control edge of the supplementary piston closes against a control edge on the valve housing on the discharge side.
By means of slight changes to the control part, which is actuated electromagnetically or by a piezoelectric actuator, which require very little labor from a production technology standpoint, it is possible to achieve a substantial improvement of the efficiency of an injection system, in particular a substantially more precise metering of the fuel quantity to be injected during the pre-injection phase in the combustion chamber of an internal combustion engine.